Catalysts for hydrodesulfurizing petrochemical intermediate products in the petrochemical industry mainly are porous inorganic materials which contain aluminum, nickel, cobalt, molybdenum and vanadium. Generally, after a long period of operation time, the catalysts become poisoned or deactivated during the hydrodesulfurization process. The disposal of the deactivated catalysts is a great concern in industry because of the pollution problems caused by the metal ions contained therein. A typical treatment prior to disposing these catalysts is to remove and recover the metal ions from the catalysts. In a typical recovering process, the poisoned catalysts are calcined in air at 400.degree.-600.degree. C. so that the organic substances deposited thereon are decomposed and removed first, and then the calcined catalysts are cooled down to room temperature and are ground to a powder form. The ground catalyst powder is soaked in a sulfuric acid aqueous solution for a period of time to leach almost all the metal ions contained in the catalyst. The resulting sulfuric acid aqueous solution normally contains vanadium, molybdenum, cobalt, nickel, and aluminum ions. This acidic solution is subjected to an extraction treatment to remove vanadium and molybdenum ions therefrom. Then the aluminum, cobalt, and nickel ions contained in the remaining sulfuric acid aqueous are separated with one another by a sequence of further extraction treatments.
Because there are far more aluminum ions than cobalt and nickel ions, most of the extractants up to the present which extract aluminum ions first, and then cobalt and nickel ions, require not only a large amount of extractant but also an extraction apparatus with a large capacity. From a technical point of view, it would be more effective and economical if the least amount species in a mixture are extracted first, and the more concentrated species are left in the final raffinate (remaining solution). Furthermore, the commercial values of cobalt and nickel are higher than aluminum; therefore, it is more logical to extract cobalt and nickel prior to aluminum ions.
U.S. Pat. No. 4,088,733 discloses a process for removing cobalt from an aqueous acid solution containing cobalt and nickel by liquid-liquid extraction, which comprises the steps of contacting the aqueous acid solution with an organic phase comprising a concentrated alpha hydroxyoxime extractant and an organophosphoric acid such as di(2-ethylhexyl) phosphoric acid.
An object of the present invention is to provide an unique extractant composition to extract nickel ions from a sulfuric acid aqueous solutions which contains aluminum and nickel ions.
Another object of the present invention is to provide a method for separating aluminum, cobalt, and nickel ions contained in a sulfuric acid aqueous solution.